Collegial - collegian - collegiate
Collegial, collegian and collegiate are three adjectives (with substantive meanings). The three mean broadly the same - 'to do with a college'. There may be something to be said, in precise academic writing, for maintaining a distinction - but you are unlikely to find many writers who do. All three are derived from the noun College, which in itself presents problems of meaning.
It may be best to reserve particular words for particular uses.
- collegiate should be the most normal in academic English. Use it for all contexts in which you mean 'as an official body' - a collegiate decision is one in which a college has agreed a common position. In American, rather than British, English, it commonly means 'to do with institutions of Higher Education': collegiate sport means what in Britain might be 'University Championships'. Collegiate can also be used for any of the other adjectival meanings associated with 'College'.
- collegial means 'of, or belonging to, a college'. It may be more rigorous to use the possessive: 'a college's buildings' may be preferable to 'collegial buildings'. Otherwise, collegiate might be the best first choice for any adjective 'to do with a college'.
- collegian (which is the oldest recorded in OED amongst these three) is best used only as a noun, to mean 'person belonging to [often a student in] a college'. (In certain local contexts, colleger and collegeman may also be used. See College (clarification of meanings).) Some special uses exist:
- In the seventeenth century, a sect of the Arminian branch of Christianity was formed known as Collegiants or Collegians (because their term for their Sunday meetings was 'College'). Should you be writing about such a recondite subject, the term Collegiant (or its Latin equivalent Collegianus, plural Collegiani) may be preferable, as being less ambiguous.
- In the nineteenth century, collegian was also used as a slang term for 'a convict', 'a prisoner', with the cynical implication that prisons are just schools for completing the education of criminals.
- 'The Collegian' is quite a common name for undergraduate and other in-house periodicals produced in places of learning with the word 'College' in their titles.